Electric terminal connection and method of making the same



March 5,1935. c. c. ABBOTT 1,993,580

ELECTRIC TERMINAL CONNECTION AND METHOD OF MAKING THE SAME OriginalFiled Dec. 3, 1929 iiii l. MA

InQencor: Charles C'Abbobb, b MW M His Attor'heg.

UNITED STATES PATENT OFFICE ELECTRIC TERMINAL CONNECTION AND METHOD OFMAKING THE SAME Charles 0. Abbott, Pittslield, Mass, assignor to GeneralElectric Company, a corporation of New York Original applicationDecember 3, 1929, Serial No. 411,372, now Patent No. 1,959,776, datedMay 22, 1934. Divided and this application February 20, 1932, Serial No.594,276

2 Claims. (01. 29-4555) My invention relates to electric terminalconsheathed wire heating unit of the type described nections, moreparticularly to terminal connecand claimed in my above-mentionedcopending 1 tions for electric heating units and the like, andapplication, Serial No. 411,372, filed December 3, has for its objectthe provision of an improved 1929. This heating unit 10 comprises astraight 5 connection between the resistance conductor of core wireresistance heating element 11 formed 5 the heating unit and a terminalmember, and from a pair of twisted resistanceconductors 110, method forefiecting the connection. 11b, extending centrally of a metallic sheath12.

Although not limited thereto, my invention has The resistance element ismade from a suitable particular application to electric heating unitshigh resistance material having considerable 1 having a resistanceheating element formed by TeSi1ien 3y,'SuCh as nickel-Chromium y- Thetwisting a plurality of resistance conductors toheating element 11 isembedded in a compacted gether as described and claimed in my copendmassof powdered heat refractory insulating maing application, Serial No.111,372, filed Decemterial 13 such as ma e u xideher 3, 1929, issued asPatent No. 1,959,776 on May Metallic terminals 14 and 15 are p vid d for22, 1934 of which this application is a division. the heating elementEach terminal i D 15 In carrying my invention into effect in one. videdwith a stepped longitudinal recess 16 for form thereof, I provide thetwisted resistance receiving a correspondingly stepped portion 17 ofconductor with a stepped terminal portion and he twisted heating ele Thepp provide in the terminal a stepped bore to receive minal D tiOn 0f eheating element is formed 20 this terminalportion. I then insert thestepped by a reduced twisted portion 17a of the end por- 20 terminalportion within the bore provided for it tion of the heating element andby the end porin the terminal and reduce the diameter of the tion 1717of one of the conductors which projects terminal so as to iorce it intogood electrical and beyond the twisted portion, preferably in the axismechanical contact with the resistance conducf the element. It will beobserved that when tors. Preferably the terminal will be reduced to theterminal portion 1'7 is inserted in the stepped 25 such an extent thatthe material of the terminal bore of the terminal, the reduced twistedPortion will be forced into the grooves between the 17a will be receivedin the larger terminal recess twisted resistance conductors. portion 16aand the projecting portion 17b will For a more complete understanding ofmy inbe received in the smaller recess portion 16b.

vention reference should be had to the accom- Each terminal iscompressed on its heating ele- 30 panying drawing in which Fig. 1 is asectional ment terminal portion so that the metal of the viewillustrating the electric heating unit of my n l s forced i the spacesor grooves above-mentioned copending application provided tween theturns of the twisted core heating elewith an electric terminalconnection arranged in ment. A very good electrical and mechanicalaccordance with my invention and showing the connection is thus providedbetween the terunit in a preliminary stage of its construction; minalsand the heating element. It will be ob- Fig. 2 is a fragmentary viewillustrating a porserved that before a terminal could be removed tion ofthe heating element of Fig. 1 in an ador pulled from the heatingelement, it would be vanced stage of the process of making theheatnecessary to strip the inner threads which are mg unit; Fig. 3 is asectional view taken through formed in the terminal recesses when theter- 40 the line 3-3 of Fig. 2; Fig. 4 is an elevation of minal iscompressed on the unit.

a portion of the twisted heating element illusv In forming the heatingunit, the electrical retrating the element prepared for connection withsistance elements 11a and 11b are twisted together its terminals; Fig. 5is an elevation of the terwith a relatively short pitch to formthe'resist- 5 minal partly in section illustrating the terminal anceheating element 11. While I have shown prepared for connection with theheating elebut two resistance strands wound about each ment; Fig. 6 is asectional view illustrating the other to form the twisted heatingelement, it is heating unit in a more advanced stage of its conto beunderstood that several, as for instance struction; Fig. 7 is anelevation of a member used three or four, may be used if desired.

in making the heating element; and Fig. 8 is a Electric connections arethen established be- 50 partial elevation of the finished electricheating tween the terminals 14 and 15 and their respecunit provided witha terminal connection artiveend portions of the heating element 11.ranged in accordance with my invention. The heating element 11 isprepared for connec- Referring to the drawing, 1 have shown my tion withthe terminals 14 and 15 by providing 1 invention in one form inconnection with a the Stepped end terminal portions 1'7. The proiectingportion 17b may be formed by cutting off or otherwise detaching aportion of one of the conductors (11a, 11b) so as to leave the singlestrand. After this, the twisted end portion 170.

of the heating element is swaged or otherwise reduced to approximatelythe diameter of the larger terminal recess portion 16a. It will beunderstood that the projecting portion 17b will be bent or twisted so asto lie in the axis of the heating element and further that the portion16b of the terminal recess will have a diameter approximately equal tothat of the projecting strand 17b so that it will just receive thisportion. The terminal portion 17 is then inserted in the recess 16 ofthe terminal, after which the terminal is swaged or otherwisecompressed, preferably to a square cross-section, so that its metal isforced into the grooves or spaces between the twisted conductors of theterminal portions 17a of the heating element.

This terminal arrangement is a very important feature of my invention.It will be understood that if the twisted core wire heating element wereleft full size to the end rather than having the stepped formation asshown, and the terminal were provided with a straight bore to receiveit, the terminal would be so weak at the end of the core wire that itwould practically draw in two at this point during the subsequentswaging of the assembled heating unit.

I provide 'the metallic sheath 12 with plurality of flattened portions12a positioned so as to. maintain the heating element central during theinsulating material loading operation and during the initial swagingoperations. The sheath at these flattened portions will be suflicientlywide to receive the heating element but ordinarily will not be largeenough for the terminals to pass through. Consequently it is generallynecessary to assemble the heating element with the sheath before theindenting operation.

The metallic sheath 12 is prepared for the assembly of the heatingelement 11, first by providing its ends with count'erbores 20 (Fig. 1)and then by thoroughly cleaning the interior of the sheath. Theresistance element 11 with its terminals attached is then insertedlengthwise within the sheath as shown in Fig. 1 and preferably is placedunder a slight tension to hold it straight within the sheath. It will beunderstood that the heating element will have a length suflicient topermit the terminals to project from the ends of the sheath. The.heating element may be supported and tensioned in the sheath'by placingwashers 21 in the counterbores 20 and which fit on the terminal membersso as to hold them centrally of the sheath. Suitable sleeves or col lars22 are then provided on the terminal members and are secured by means ofnuts 23 which are turned on the threaded projecting end portions of theterminals. It will be understood that by turning the nuts 23 inwardly onthe terminal portions, the heating element will be placed under atension suificient to hold it central within the tube and to prevent itskinking during the indenting operation.

After the heating element has been assembled with the sheath as shown inFig. 1, the sheath is ready for the indenting operation. As shown (Figs.2 and 3), the indents are placed in the metallic sheath so as to providethe flattened portions 12a in pairs with the axes of the adjacentportions positioned substantially at right angles to each other. It willbe observed that by reason of this arrangement, the reduced portions ofeach pair taken together form a square-shaped retaining section aroundthe resistance element, (Fig. 3). It will be understood that a number ofthese pairs will be spaced at intervals along the length of the sheath.

It will be observed by reference to Fig. 3 that the passageway throughthe sheath at these flattened portions is sufliciently large to receivethe heating element 11 and by reason of the fact that the adjacentflattened portions are arranged substantially at right angles to eachother, the heating element will be secured centrally of the sheath at aplurality of points spaced at intervals throughout its length. However,it is very important that the reduced sections of the sheath besufiiciently large to prevent gripping of the resistance element at anypoint. Thus, generally there will be some clearance between the walls ofthe sheath and the element. It is preferable, therefore, to form eachpair of flattened portions in the sheath at substantially'45" to theadjacent pairs. In other words one pair of indents will be formed withtheir axes substantially at 90 to each other. Then the sheath will berotated about its longitudinal axis through 45 and another set ofindents will be formed with their axes substantially at 90 to eachother. In effect, therefore, the four indents of adjacent pairs takentogether will form an octagonal shaped retaining section. Thisarrangement precludes any possibility of the element moving from itscentral position beyond the limits defined by the clearance between theresistance element and the side portions of the two square retainingsections formed by the adjacent pairs. It will be understood, of course,that ifthe axes of the flattened portions of each pair were not thusrotated relatively to the axes of the corresponding flattened portionsof the adjacent pairs, the limits of the clearance would be defined bythe distance between the surface of the resistance element and thecorner portions of the square retaining sections.

It will be understood that the flattened portions will be spaced so thatthe heating element will be properly centered within the sheath but willnot be positioned so close to each other that the passageway through thesheath will be restricted. Moreover, it will be understood that theindents will be placed in the sheath not only to maintain theheatingelement 11 central but also to maintain the terminal members 14and 15 centrally of the sheath (Fig. 6).

After the sheath has thus been indented, the nuts 23, the sleeves 22 andthe washers 21 are removed and the interior of the sheath is thoroughlycleaned so that any scale which might have become loosened by theindenting process is removed. The interior may thus be cleaned byblowing dry air through the sheath.

The sheath is now ready for the loading operation. The sheath is closedat one end, for example at the left hand end, as viewed in Fig. 6, by apair of solid washers 21 which flt on the terminal 14 so as to hold theterminal centrally of 'the tube. These washers, as shown, are receivedin the left hand counterbore 20. The sleeve 22 is then positioned on theprojecting end portion of the terminal 14 and is secured by means of thenut 23. The terminal 15 is secured in a similar manner centrally of thesheath by means of a triangular shaped washer 26 which is positioned inthe counterbore 20 at the right hand end of the sheath. The resistanceconductor 11 is. placed under a slight tension by turning the nuts 23inwardly onlthe terminals.

The sheath is now filled through the openings provided by the triangularwasher 26 with the heat refractory powdered insulating material 13. Toaccomplish this, the sheath is held in an upright position in a specialvibrating machine (not shown) with the end provided with the triangularwasher uppermost. As the sheath is filled with the insulating materialthrough the openings provided by the triangular washer, it is vibratedto shake the insulating material together and distribute it uniformlyaround the terminals and the resistance element. Itwill be understoodthat the powdered insulating material will readily pass through theflattened portions 12a to the lower portions of the upright sheath. Whenthe sheath has been filled, a solid washer 27 which is similar to thewashers 21 is inserted ,in place around the terminal 15 to close thesheath. The sleeve 22 and the nut 23 are then replaced and-the core wireresistance element 11 is placed under a slight strain by turning the nut23 inwardly on the terminal 15/ The ends of the sheath are .then turnedover so as to aecure the washers in the ends of the sheath.

After the sheath has thus been loaded with the powdered insulatingmaterial, I compact the magnesium oxide in these portions of the sheathbetween the flattened portions 12a. aroundthe core wire heating element.This further insures the central location of the heating element.

This compacting of the insulating material may be accomplished bystriking the metallic sheath between each pair of flattened portionswith a rather heavy impacting blow, as by hitting the sheath with ashort split die in a press. It has been found that this operation socompacts the magnesium oxide around the core wire that it .will be heldperfectly central within the sheath during the-swaging operations. Afterthe insulating material has thus been compacted, the nuts 23 and thesleeves 22 are again removed.

The entire unit is now passed through a swaging or rolling machine forthe purpose of compacting the insulating material within the sheath to ahard dense mass, the swaging operation reducing the diameter andincreasing the length of the unit. Several through the swaging machinegenerally will remove the fiattened portions of the sheath bulging theflattened sides outward somewhat, and it has been found that the sheathwill assume a complete cylindrical shape throughoutits length. Thesheath will lengthen somewhat faster than the core wire during the firsttwo or three passes through the machine. minals will be drawn within thesheath for a short distance. However, the insulating material willgenerally be sufilciently compacted by the first several passes tosecure the terminals against further inward movement. core wireresistance during the swaging operation will be lengthened so that theoriginal relatively short pitch of the wire will be greatly increased.Thus in one specific heating unit, the pitch which was approximatelybefore swaging was increased by the swaging operation to approximatelyH". Moreover the'terminals 14 and 15 In other words, the projecting ter-The twisted are gradually reduced in diameter by the swagins. therecessed ends contracting around the resistance element.

It will be understood that if desired the heating unit may be annealedbetween successive swaging operations in order to prevent the resistanceelement and sheath from becoming hard and brittle.

After the unit has been swaged to the desired extent, the washers ateach end are out oi! or otherwise removed and the ends of the unit aresquared oil (Fig. 8). It will be understood that the terminals 14 and 15will be held firmly in place by the compacted insulating material inwhich they are embedded.

While I have shown a particular embodiment of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made, and I, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. The method of securing a terminal to an elongated electricalconductor formed of separate elongated conductors twisted togetherthroughout their lengths, which comprises forming a stepped terminalportion on said conductors by projecting one end portion of one of saidconductors axially beyond the twisted end portion of said conductors,providing in a solid metallic terminal member .a stepped borecorresponding to the stepped terminal portion on said conductors,fitting said terminal portion of said conductors -into said stepped borein said terminal member and then'swaging said terminal member onto saidterminal portion so that said terminal member tightly grips saidterminal portion with good electrical and mechanical engagement, theprojecting portion of said stepped terminal portion gripped by thecorresponding part of said terminal member relieving the strain in thewalls of said terminal member at the bottom of the larger part of saidstepped bore set up when a force is applied to said conductors tendingto remove them from said terminal member, thereby preventing rupture ofsaid terminal member at the bottom of said larger bore portion.

2. In a terminal, a plurality of electrical conductors twisted togetherthroughout their,

lengths. a stepped terminal portion on said conductors defined by one ofsaid conductors extending axially from the twisted portion of saidconductors, and a solid metallic terminal member provided with 'astepped bore corresponding to the stepped terminal portion on saidconductors fitted onto said terminal portion and compressed thereon ingood electrical and mechanical relation with it, the reduced part ofsaid terminal portion gripped by the corresponding part of said terminalmember relieving the strain in the walls of said terminal member at thebottom of the larger part of said bore set up when a force is applied tosaid conductors tending to remove them from said terminal member,thereby preventing rupture of said terminal member at the bottom of saidlarger bore portion.

. CHARLES C. ABBO'I'I.

